[Gllug] 64K Channels and all that ...

Dave Cridland dave at cridland.net
Thu Sep 19 23:31:05 UTC 2002


On Thu, 2002-09-19 at 23:47, Chris Bell wrote:
> On Thu 19 Sep, t.clarke wrote:
> > 
> > Just out of interest, we have a connection through a Cisco ISDN router I think,
> > to the UK Customs facility (PACE) which uses the D channel in the manner
> > described.  If I recall correctly, when the other end wants us to collect data
> > they send some kind of control packet over the permanently on D channel which
> > causes the router to 'dial out' over one of the 64K channels and initiate a
> > connection to the host computer.
> > 
> > Out of total curiosity, does anynone know how ISDN data (being synchronous ?)
> > is 'framed' so that each byte is recognised ??
> > 
> > 
> > Tim
> > 
>    A quick look at the reference book says that basic rate ISDN has two 64K
> B (Bearer) channels plus one 16K D (Data) channel, while Primary rate ISDN
> has 23 B channels plus one D channel. The D channels carry the control data.
> It is possible to link any B channels on demand for faster data
> transmission.

You in the US or something? ;-)

An E1 PRI has 30 'B'earer channels and one 'S'ignalling channel - an S
channel is, as far as I can work out, a 'D'ial channel with a funny
name.

A T1 has fewer Bs, and they're 56k in the states, hence the K56 modems.
They could be K64 in the UK. Except nobody ever gets more than 40k
anyway, and that only on a good day. :-)



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